This invention relates generally to photodetector systems responsive to ambient light, and more particularly, to a photodetector system wherein the electrical output signal is responsive to the position of a light source with respect to a location distal from the photodetector.
In some light sensor arrangements, particularly of the type used in vehicles, it is desired that the direction of incident light be determined by a photodetector device located at a distance from the point at which the monitoring of the light is desired. It is desired that sunlight impinge upon a diffuser located about one and one half inches from the light sensor device.
The diffuser overlies a plurality of sensors each covering a respective zone of the field of view desired to be monitored. In an embodiment where four sensors monitor four respective zones, the sensors are tightly packed and each diffuiser and its corresponding light sensor employs a dedicated hollow tube, along which the light from the diffuser is propagated.
A significant problem is the transmission of a sufficient amount of light down the connecting tube that would reach the photodetector. The surface finish of the tube is very important. Initially, it would appear that a diffuse finish, which would scatter the incoming light in many directions, would effectively cause the light to be propagated along the hollow tube. However, by using a polished surface on the inside of the tube, the amount of light that reaches the photodiode is increase dramatically. A highly polished tube functions almost like a mirror. In fact, if the light were parallel to the tube, a perfectly polished surface would behave exactly like a perfect mirror. The phenomenon is called grazing incidence.